In recent years, conductive circuit patterns on printed wiring boards are becoming finer and finer with increasing positional accuracy; furthermore, surface-mounted components are becoming smaller. This trend promoted the widespread use of photosensitive resin composition-based photolithography in the manufacture of printed wiring boards. Resin compositions which contain epoxy compounds as one of photosensitive resins (see Patent Documents 1 and 2) have been widely used as materials of solder resists that serve as permanent protection films for metal interconnections. Moreover, resist compositions containing carboxyl group-containing binder polymers have been widely used for the manufacture of interconnections (see Patent Document 3).
Either of the above resin compositions is used during metal plating as a material for masking portions where plating is not intended. However, recent studies indicate that these masking materials are less durable under stringent metal plating conditions. Thus, demand has particularly arisen for materials which are durable enough to be capable of being used under stringent metal plating conditions, such as electroless gold plating condition where plating is conducted under acidic condition at elevated temperatures (70° C. or higher), electroless tin plating condition where plating is conducted under strong acid condition, etc.
It is reported that an excellent electroless plating layer can be obtained by providing an additional photosensitive resin composition layer on a solder resist followed by plating and removal of the photosensitive resin layer (see Patent Document 4). However, it is not industrially desirable to provide such a protection layer only for the purpose of achieving electroless plating. Thus, there is a strong demand for materials with high plating resistance.
Photosensitive resins with excellent insulating property and excellent metal adhesion have also been required. To meet this requirement, technologies have been suggested by which adhesion of photosensitive resins, which contain polyimide resin and polybenzoxazole resin as highly-insulating resins, to metal interconnections is improved (see Patent Document 5). However, while photosensitive resins obtained with these technologies can be developed by unstable aqueous solutions of organic base compounds, they cannot be developed at all with low-concentration alkali metal aqueous solutions—typical developers used in the manufacture of printed wiring boards. For this reason, these photosensitive resins may be disadvantageous in industrial uses.    Patent Document 1: International Application Publication No. WO02/24774    Patent Document 2: International Application Publication No. WO03/059975    Patent Document 3: Japanese Patent Application Laid-Open No. 2000-321767    Patent Document 4: Japanese Patent Application Laid-Open No. 2006-330193    Patent Document 5: Japanese Patent Application Laid-Open No. 2006-227387